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Eur J Cardiothorac Surg 2001;19:827-833
© 2001 Elsevier Science NL
a Cattedra of Cardiac Surgery, University of Florence, Florence, Italy
b IRCCS NEUROMED, Via Atinense N.18, 86077(ISERNIA), Pozzilli, Italy
Received 15 January 2001; received in revised form 26 February 2001; accepted 19 March 2001.
Corresponding author. Cardiochirurgia, University Hospital of Florence Careggi, Viale Morgagni, 85-50134 Firenze, Italy. Tel: +39-3389855782; fax: +39-554277458
e-mail: mbonacchi{at}hotmail.com
| Abstract |
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Key Words: Bilateral internal mammary artery Coronary revascularization Respiratory dysfunction
| 1. Introduction |
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Respiratory complications are one of the most frequently found complications during CABG surgical procedures [12]. The causes of postoperative respiratory complications are different and depend on anaesthesia, cardiopulmonary bypass and the surgical techniques [13]. Furthermore, it is noted that the employment of the IMAs versus only vein grafts increased the pulmonary complication incidence and postoperative pain after CABG surgery, inducing a worse postoperative outcome [14,15].
Different techniques have been employed for IMA harvesting, such as the pedunculated, skeletonized and semi-skeletonized techniques. Some surgeons prefer to open the pleural cavity during the IMA harvesting for better exposure of this arterial conduit.
The aim of this study was to evaluate the influence of open pleurae and the type of IMA harvesting technique used on the postoperative respiratory functional status and thoracic pain in patients undergoing CABG employing both IMAs.
| 2. Materials and methods |
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2.1. Patient characteristics
These are given in Table 1. There were no differences according to the preoperative cardiac status and associated pathologies, spyrometric and blood gas analysis data between groups.
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2.3. Surgical techniques
IMAs were harvested according to the SKT as previously described [11]. After a median longitudinal sternotomy incision, the mediastinal pleurae were dissected gently from the endothoracic fascia, meticulously avoiding their damage. Then, the endothoracic fascia was incised medially and the IMA and both satellite veins were visualized. The IMA was separated from the chest wall and isolated from the fascia, the veins satellite and adipose tissue. Sternal, pericardial and anterior intercostal branches were ligated with small-sized haemostatic clips frequently, only by the IMA side. The left (LIMA) and right (RIMA) internal mammary arteries were harvested in a skeletonized fashion until the origin at the subclavian artery, just the terminal branches, without opening the pleural cavities. The IMA's stem is left intact to allow blood flow through until it is ready for use and covered with gauze impregnated with warm (3740°C) papaverine solution (4 mg/ml), which allows a pharmacological dilatation. In both sides of the superior mediastinum, the pleurae-pericardial tissues were dissected and the IMA beds were created.
The IMAs were mobilized through these beds and penetrate into the pericardial cavity anterior to the phrenic nerve. The IMA's bed allows it to lie median and posterior to the lung and the ventilation does not produce any stretch or distortion of the arteries, and these are protected should resternotomy be required. Routing of the RIMA behind the superior vena cava and further into the transverse sinus allows additional length, thereby facilitating the grafting of the marginal obtuse coronary arteries via a less circuitous and more protected route. The internal blood pressure will force the graft to always have the right orientation to avoid graft distortion. In cases where the pleural cavity was opened incidentally, the pleural cavities were drained separately.
When IMAs were harvested according to the PKT, the pleurae were opened, and the internal thoracic fascia, muscle and fat tissue containing IMA and concomitant veins was incised with the electrocautery along both sides of the IMA, 0.51 cm away: next, the pedicle was dissected working from its distal to proximal end and the major IMA branches were clipped by haemoclips. The pedicle is wrapped in gauze soaked with warm papaverine solution. After heparin was administered, the IMA was cut, the distal end was closed by transfixing ligation and clamped proximally with a bulldog, and, until initiation of the grafting procedure, recovered with the gauze impregnated with papaverine solution. At the end of intervention, a large drain tube is located in the pleural cavities (3032 F), draining separately under aspiration (-20/-30 cm H2O).
The pericardium was opened, the aorta and right atrium were cannulated in the usual fashion, and cardiopulmonary bypass was started. Normothermia or moderate hypothermia (32°C) was employed during cardiopulmonary bypass. The intermittent anterograde cold crystalloid cardioplegia technique was employed in intervals of 3040 min. Fifty-three (group I), 62 (group II), and 19 patients (group III) underwent total arterial myocardial revascularization. Eighty-seven of them underwent arterial myocardial revascularization according to the previously described techniques [11,16]. Intravenous nitro-derivate therapy was initiated immediately after the aorta was unclamped, according to the haemodynamic situation, and was continued during the postoperative course in the intensive care unit and eventually combined with diltiazem. Oral vasodilator therapy was continued for 4 postoperative weeks.
The intraoperative data are given in Table 2.
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The ventilation technique was identical in all groups. During cardiopulmonary bypass, the lungs remained collapsed.
2.5. Postoperative ventilation
In the intensive care unit, the patient management protocol included:
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moderate pain) were treated with morphine and ketorelactromentamina (FANS). Chest tubes were left in situ until 12 postoperative days. On the second postoperative day, central and arterial lines and the urinary catheter were removed, and the patients were mobilized.
The criteria for hospital discharge were: normal pulse and arterial pressure, no pyrexia and leucocytosis, haemoglobin >8 mg/dl, creatinine, transaminases and electrolytes in range, normal ECG and chest X-ray.
In this study, postoperative spyrometry evaluation was not performed.
2.6. Definitions
Hospital mortality was defined as death for any reason occurring within 30 days after operation. Perioperative myocardial infarction was defined as the appearance of new Q-waves or a significant loss of R-wave forces peak creatine phosphokinase MB fractions of greater than 10% of the total CK. Low cardiac output syndrome was defined as a cardiac index of <2.0 l/min per m2, requiring pharmacological support and/or contropulsation. Postoperative renal dysfunction was defined as an increment in the creatinine level of
1 mg/dl compared with the preoperative value. Gastrointestinal complications included a confirmed diagnosis of upper and lower gastrointestinal haemorrhage, intestinal ischaemia, acute cholecystitis and pancreatitis.
2.7. Statistical analysis
Group statistics are expressed as means±1 SD. The MannWhitney test was used for continuous variables. Fisher's Exact test was used for non-parametric variables. Multivariate analysis was performed by the long-rank test. Significance between data was considered achieved when P<0.05.
| 3. Results |
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Postoperatively, we found a similar incidence of cardiac, neurological, gastrointestinal and renal complications between groups. Six (7.5%) patients in group I versus 34 (19%) in group II bled more than 1000 ml during the first operative day (P<0.028), but the incidence of re-thoracotomy for bleeding was the same between groups (Table 4). The mean blood transfusion/patient was similar between groups, due to the re-employment of the lost drained blood re-transfusion using appropriate closed systems. The intensive care unit stay was significantly higher in groups II (P<0.005) and III (P<0.002) versus group I.
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Pulmonary complications and the respiratory functional status were analyzed in all patients.
The mechanical ventilation time was significantly higher in groups II and III versus group I: 6.2±2.9 and 6±1.1 h, respectively versus 5.4±1.2 h (P<0.018 and P<0.02). The incidence of prolonged ventilation for >24 h (P=0.03), pre-extubation necessity of assist pressure of
20 cm H20 (P=0.001), unilateral pleural effusion (P=0.011), postoperative thoracocentesis (P=0.027), atelectasis during the intensive care unit period (P<0.013) were significantly higher in group II versus group I. Instead, only the incidence of postoperative thoracocentesis (P<0.027) was significantly higher in group III versus group I. There were no differences between groups II and III regarding postoperative pulmonary complications. The incidence of haematic versus serous pleural effusion was significantly higher in groups II and III versus group I (P<0.003 and P<0.01, respectively; Table 3).
Arterial gas analysis, according to our protocol, demonstrated a significantly depressed respiratory function during mechanical ventilation in groups II and III (Table 3). In all measurements during mechanical ventilation and within 4 h after extubation, the patients of groups II and III necessitated a significantly greater FiO2 to attain acceptable PaO2 and PaCO2 arterial levels. Even though the arterial blood gas analyses were within normal levels postoperatively in all groups, the outcome in terms of higher PaO2 and lower PaCO2 under a lower FiO2 was significantly better in group I compared with groups II and III. From all of the blood gas variables, it seems that PaCO2 is the most discerning variable. There were no differences regarding the arterial blood gas analyses between groups II and III (P=ns). The arterial blood gas data analysis results were similar in both groups (P=ns) at 5 days after the surgical procedure (Table 3).
| 4. Discussion |
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We have previously employed the SKT for IMA harvesting [11,16]. Even in this series, the number of patients undergoing total arterial myocardial revascularization and the number of the arterial composite grafts were significantly higher in patients undergoing IMA harvesting according the skeletonized approach with closed or opened pleurae. This technique provides more conduit length, and as a consequence, the possibility of composite graft construction, than the PKT.
Other reports have demonstrated that IMA harvesting during CABG surgery is an adjunctive factor for further impairment of postoperative pulmonary function [12,13,17]. Taggar et al. [18] hypothesized that one possible explanation of the post CABG surgery respiratory dysfunction is the general inflammatory response induced by cardiopulmonary bypass and pulmonary interstitial alterations. Perhaps this hypothesis alone is insufficient for explaining all the post CABG surgery pulmonary alterations. The optimal management of the lungs during CABG surgery remains to be defined. The authors opinions regarding the effect of bilateral IMA grafts on respiratory function are controversial. Some authors found an increased incidence of postoperative pulmonary complications and others did not find any difference in the arterial blood gas and respiratory complications in this pool of patients [14,1820]. Other authors noted a positive effect on postoperative pulmonary function when the pleurae remained intact during IMA harvesting for CABG surgery [2123]. Nevertheless, there is no proper study regarding the role of the integrity of the pleurae in postoperative respiratory dysfunction in patients undergoing harvesting of both IMAs for CABG surgery.
In our series of 299 patients, we found significantly higher bleeding in patients undergoing IMA harvesting according to the PKT, probably due to the more extensive dissection of surrounding tissue during the surgical procedure of IMA harvesting. Another factor that may explain such a result could be the incomplete visualization of the IMAs and unclipped mammary vein collaterals in patients undergoing IMA harvesting according to the PKT. Also, the unilateral pleural effusion and thoracocentesis incidence was higher in patients undergoing IMA harvesting by the PKT with open pleurae. In most of the cases in this group of patients, the pleural effusion was haematic, in contrast to the most frequently found serous effusion in patients undergoing IMA harvesting by the SKT with intact pleurae. We hypothesized that these differences depend, in part, on the surgical technique for IMAs preparation. Opening the pleurae induces the mediastinal blood loss to shift in the pleural cavity, increasing the pleural effusion quantity. In our study, IMA harvesting with intact pleurae demonstrated a significant pain reduction within the first hours after the surgical procedure. The reduction in the subjective estimation pain score was significant after 112 h after awakening, becoming non-significant after the thoracic drains were removed. The lack of a significant difference in the pain score within 60 min after awakening reflects primarily the effect of the intraoperative anaestheticanalgesic treatment. In the postoperative period, the combination of pain reduction and the limited use of morphine and FANS in patients with intact pleurae may induce less pulmonary function impairment. These findings demonstrate clearly that the chest tubes, inserted in the pleural cavity due to the intraoperatively opened pleurae, is a supplementary factor inducing a painful inspiration and greater respiratory dysfunction.
The opened pleurae negatively influenced blood arterial gas concentrations, resulting in a lower PaO2 and higher PaCO2 and FiO2 during the mechanical ventilation and in the first hours after extubation, returning to similar levels only during the fifth postoperative day. Even though the arterial blood gas analysis results were within the acceptable postoperative values in all patients, independently of the opened or intact pleurae, the FiO2 level was significantly higher in patients with opened pleurae. The analysis of the arterial blood gases revealed less significance between patients undergoing IMA harvesting by the SKT with intact or opened pleurae than between patients undergoing IMA harvesting by the SKT with intact pleurae and IMA harvesting by the PKT with opened pleurae, but we do believe that this was due to the small number of patients undergoing skeletonized IMAs with incidentally opened pleurae that were included in this study. The incidence of thoracocentesis and atelectasis was significantly higher in patients undergoing CABG with open pleurae, revealing a higher morbidity in this pool of patients compared with those undergoing CABG surgery with intact pleurae.
In conclusion, based on such results, we may say that the pleural integrity has beneficial effects on the respiratory functional status after CABG using bilateral IMAs. A meticulous and more delicate IMA harvesting approach significantly reduces the postoperative morbidity regarding the pulmonary functional status, and as a consequence, reduces the hospital costs. We did not find any differences in the respiratory function related to the type of IMA harvesting technique employed.
Study limits included: (1) a small number of patients undergoing IMA harvesting according the SKT with opened pleurae; (2) we did not perform mechanical respiratory tests postoperatively, but we do believe that longer mechanical ventilation and assisted pressure times in patients with opened pleurae demonstrate indirectly that the pleural integrity improves the respiratory mechanics during the postoperative course; (3) even though we do not have exact figures regarding the hospital costs between patients with opened and intact pleurae, we may say that a significant reduction of the mechanical ventilation, intensive care unit stay, lower postoperative morbidity in terms of the thoracocentesis and atelectasis incidence in patients with intact pleurae are significant indicators demonstrating lower hospital costs in this pool of patients.
| References |
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